Method of and means for generating low-frequency electrical oscillations



E. 0i SCRIVERE.

METHOD QF AND MEANS FOR GENERATING LOW FREQUENCY ELECTRIC/al GS xldg UNITED STATES PATENT OFFICE.

EDWARD O. SCRIVEN, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRIC COMPANY, INCORPORATED, OF NEW YORK, N. Y., A

YORK.

CORPORATION F NEW METHOD OF AND MEANS FOR GENERATING LOW-FREQUENCY ELECTRICAL OSCILLA- TIONS.

Application filed September 21, 1918.

T 0 all 107mm t may concern.'

Be it known that I, EDWARD O. SoRIvEN, a citizen of the United States, residing at N ew York, in the county of New York, State of New York, have invented certain new and useful Improvements in Methods of and Means for Generating Low-Frequency Electrical Oscillations, of which the following is a full, clear, concise and exact description.

This invention relates to methods of and means for generating low frequency electrical oscillations and more particularly to oscillation generators of the vacuum tube type.

An obj'ect of the invention is to provide means for generating low frequency oscillations, which permits the regulation of the frequency of the oscillations generated.

Another object of the invention is to provide a low frequency oscillation generator of the type having no moving parts, and which does not require associated inductances or capacity elements of excessive size.

A further feature of the invention relates to an arrangement whereby two oscillation generators supply oscillations of slightly different frequencies to a detecting or combining device from. the output circuit of which oscillations of the low difference frequency maybe derived.

An additional feature of the invention relates to an arrangement for keeping two oscillation generators out of step. As is well known, there is a tendency for two periodic (lriviug forces of slightly different frequency, to get into step, if connected so as to react upon each other.A According to the present invention, this tendency is overcome by coupling the oscillators non-reactively.

If the input and output circuits of an amplifying or repeating device are so related that energy is fed back from the output to the input circuit, it is possible to produce oscillations if the physical and electrical constants of the amplifier or repeater and the electrical constants of the associated circuits are properly proportioned.

I The feed back coupling may be either electromagnetic or electrostatic and in the case of Yacuum tube amplifiers, the coupling effected through the internal capacity between elements or electrodes of the tube itself may be considerable. It is usually Specification of Letters Patent.

Patented N ov. 2, 1920.

Serial No. 255,134.

desirable to have a tuned circuit as a portion at least of either the input circuit, the output circuit, or both. Such a tuned circuit may be made to substantially' determine the frequency of the oscillations generated. If a generator ofthis type were to be used for direct production of oscillations of low frequency, the tuned circuit would necessarilv be of large natural period, thus involving either reactance elements of excessive size or magnetic core inductances. lVhere magnetic inductances are used, the wave generated is not in general, sinusoidal, and its form is variable under different conditions, for the reason that the magnetic characteristie of iron and other materials used in magnetic cores is not linear.

The present invention provides a method of and means for obtaining low frequency oscillations of practically sinusoidal wave form by the interaction of two sets of oscillations which differ in frequency by the low frequency desired. lVhen two set-s of different frequency oscillations are supplied to the input circuit of a repeater having a non-linear relation between input voltage and output current, the effect of the repeater is to combine the input frequencies in such a manner as to give their sum and difference frequencies as components of the output circuit current. The difference frequency component may b'e selected and applied to any work circuit.

In the drawing, Figure 1 illustrates diagrammatically one arrangement of circuits for producing low frequency oscillations and Fig. 2 illustrates a modification of the arrangement of Fig. 1.

Referring to Fig. 1, a highly evacuated tube 1 contains a hot filament 2 or other source of electrons, a plate electrode or anode 3 and a grid or impedance controlling element 4. A similar evacuated tube or bulb 5 contains a cathode 6, an anode 7 and a grid 8. Cathodes 2 and 6 may be heated by a common current source 9. The grid-filament circuit of tube 1 includes an inductance the plate-filament circuit includes an inductance 11 inductively coupled to inductance 10, and asource 12 of space current may be common to the output circuits of both tubes. A large capacity element 13 is shunted around the source 12 toy furnish low impedance path for high frequency currents. A capacity 111 connected between the grid and plateter- \minals completes a closed oscillatory cir- 'related. The closed oscillatory circuit of tube includes elements 13, 17, 15 and 16. The reactance of capacity element 13, which is common to the two oscillatory circuits is very small and accordingly this element does not serve to couple the two circuits in such a manner as to cause reaction of the one upon the other.`

A combining device 18 consists of a highly evacuated tube containing a hot cathode 19, a grid 20 and an anode 21. A conductor 22, which includes three high resistance elements R1, R2, R3, and a polarizing electric current source 23 connects the grid 4 to grid 20, a conductor 25 including a high resistance R, connects the grid 8 to the terminal of source v 23 electrically remote from grid 20, and a conductor 26 connects filaments 2 and 6 tov filament 19.v Bridged across the conductors 22 and 26 are two closed tuned circuits LlCl, L2C2, each tuned to the frequency of the oscillations producedby the oscillator comprising tube 1 and its associated circuits. The space current path of the output circuit of tube 18 includes a source 27 of space current in series with a choke coil 28. The low frequency oscillation output circuit 29',

- 30 -to which the load or work circuit may be connected, is connected directly to the plate and filament respectively, a blocking condenser 31 of large capacity serving to prevent passage of direct current from source 27 to the load. A small capacity element 32 bridged across the output circuit offers low impedance to high frequency oscillations and high impedance to oscillations of the frequency which it is desired to produce and supply over the output circuit 29, 30.

rllhe operationv of the circuit arrangement illustrated in Fig. 1 is as follows :v 'lfube 1 and its associated input and output circuits serves as a source of high frequency oscillations, the frequency of which is determined largely by the vfrequency of the circuit 11, 13, 10, 14 and oscillations of this fixed frequency are supplied over the conductors 22 and 26 to the input circuit of combining device 18. Tuned circuits LlCl, L2C2, each offer substantially infinite impedance to the fundamental frequency thus supplied but low impedence to harmonics which are therefore shunted out from the input circuit of tube 18 and largely dissipated by the partie ular resistance elements l or thfoujjf resaca? which they pass. rlhis feature is important for` if each oscillator delivers not 'only a fundamental vfrequencybut harmonics as well, low frequency oscillations which are harmonics of the desired low frequency will be obtained in the output circuit of-'the combining device. The suppression of harmonics of one of the fundamental frequencies will prevent the production of harmonics of the desired low frequency beat oscillations. Although harmonics of one fundamental may produce with the other fundamental combination oscillations of other frequencies, these will all be of an entirely different order and may be easily suppressed or eliminated. It is therefore unnecessary to prevent the production of hailzonics of both fundamentals. rll`lie resistance Pf serves to keep the elements of the tuned circuits LlCl, lLZCZ, and those of oscillator 5 from affecting the period of the oscillatory circuit associated with generator tube 1. ln practice each of the resistances R1, R2, R3, may be of several thousand ohms so that they effectively separate the oscillatory circuits of the two generators. tially pure fundamental wave will be delivered from generator 1 to combiner 18. The' oscillator tube 5 has an oscillatory circuit, the period of which may be varied by variation of capacity element 15, and the frequency of the oscillations generated thereby is made different from that of oscillations supplied by oscillator 1 by the value of the desired low frequency. lf, for example, the

' be arranged to indicate difference frequencies directly. Oscillations are supplied by oscillator 5 over conductors 25 and 26 including a high resistance R, which serves in general the same purposes as resistances R1, R2, and R3, and also to attenuate oscillations from source 5 to substantially the same degree that those from oscillator 1 are attenuated.

Oscillations ofthe two different high frequencies are thus supplied to combiner 18 which preferably has a non-linear relation between o utput current and input electromotive force. Oscillation current components of both the sum and difference frequencies of the two sets of impressed oscillations will appear in the output circuit. Choke coil 28 excludes both oscillation components from its path and capacity element 32 excludes low frequency components which are therefore impressed upon circuit 29, 30.

ln Fig. 2, oscillator 33 is in every respect like oscillator 1, and oscillator 3e corre- It follows that a substanspends to oscillator lesistances itl, and tuned circuits 35 serre respectively to per form the same functions as resistances l, R2, Rm and circuits Llh, LEC, of lllig. l, circuits 35 each being tuned to the frequency of the oscillations produced by oscillator A modulator or combiner 3G comprising two tubes 38 is used to produce oscillations of the difference frequency. The characteristic of the combiner 3G is such that the two tubes 38 amplify symmetrically impressed input electromotive forces to the same degree, and balance these amplified variations against each other in their common output circuit, so that between. the points 37 there will be no difference of potential of the frequency of the symmetrically impressed rariations,1 TJnder these circumstances no resulting` curreut of this frequency will. flow between points 3T. l i

anothei1 electronic/- tive force is applied nsymmetrically to the combiner device, that is in such manner as to tend to make one grid positive and the other negative with respect to their common cathode connection, the amplifying power of one tube is increased and that `the other decreased so that the amplified variations of the symmetrically impressed input electromotive force variations nolonger balance in` the output circuit of the modulator and resultant oscillation component of the frequency of the symmetrically impressed electrometive force, varying in amplitude in accord ance with the unsymmetrically impressed electromotive force appears, and oscillations of this character will be transmitted thereby. As is well known, such a varyingw amplitude current may be resolved into two components one of which has the frequency sum, and the other, the frequency difference of the two impressed electromotive forces.

Oscillations aresymmetrically impressed from source 33 acrlss a circuit wl'ch is tuned to their frequency and serves as a high impedance to 'this frequency in the common portion of the input circuits of tubes 38 oscillations are impressed source by output 'windings 39 upon input windings 40 inductivcly related thereto. ilource l cordingly impresses oscillations unsymmetrically upon the tubes 38 since it tends to malte the grid of one tube positive and at the time to make the grid of y other negativfr with respect to their cathodes. is in case of the single tube combining dei/ice Fig. l, blocking condensers all of f pacity are provided to prei/ent flow of ini directional f t te load,J and i capacity el'V c provided i i a path of low impedace the sum component, The load or w may be connected across the o'i 43 and oscillations of the difference quenc of those supplied by sources 34 Will be supplied thereto, The oper nt will he clear from the in connection with Fig. l. specific circuit afrrangements hai if illustrated and described, it is to he understood that the invention is not to be limited to these particular arrangements as a whole or to their specific features, but covers all such modifications and rear rangements as fall within the scope of the appended claims.

l.What is claimed is:

l. A system for the production of oscillations of lou frequency comprising' means for generating' oscillations of two dilferent frefor preventing` reaction beeen said generating means, and means for combining said oscillations to produce oscillations of their difference frequency.

flor of lou' frcipieiufy oscillae i leans for generating high i *,ueney oscillations of two different frequencies, means for preventing reaction between said generating means, and means for combining` said high frequency' oscillations 'to produce oscillations of their dilference frequency.

n 3; system for the production of oscillar4,ons of or' freepiiency comprising means for oscillations of two different freoueidei for combining said oscillations to oscillations of their difference frequ f "d means including two Vacuum tub their output circuits connected cpo the characteristic of each of said tube such that the relation between A' in vthe output circuit and the electromoti've force impressed upon the input circuit is non-linear.

ll. il generator of low frequency oscillas comprising two sources of high frequency oscillations, a common circuit coneted to said sources, and a high resistance said circuit, 3. The combination oftwo oscillators, a

circuit connecting each of said oscillators to a common oscillation supply circuit, and a resistance of constant value permaif connected in one of said connecting s produced by one of said oscillators transmitted to said oscillation l circuit,

Y combination of means for produc- .tio..s of two different frequencies,

s i proventing,- harmonics of the oscilmeans for suppressingl harmonic oscillations of one of said frequencies, and means for combininlgr said oscillations of different frequencies to obtain oscillations of their difference frequency. v

9. ln a system for producing low frequency oscillations a combining` device comprising two electron discharge tubes, each havintgr an input circuit including a trans former winding, a common portion of said input circuits including' a closed tuned circuit, means for inducing oscillations of one frequency in said transformer winding, and means for impressing oscillations of another frequency` across said tuned circuit,

l() 'l he method of producing low frequency oscillations which comprises generating oscillations of one frequency, suppress- EDW'ARD O. SCRXVEN. 

